Access: how do you test for a blank sub form?

Hello,

I would like to test an Access sub form using VBA to see if it's empty. If it is, I would like to modify controls on the main form.

The sub form does not allow edits, additions, or deletions. How do I test the sub form to find out when it's empty? Also, do I use the test in the main form onCurrent event?

Thanks